If you’re reading this post, most likely you encounter the following error while adding domain in your cPanel.
"Sorry, subdomains of the hostname cannot be parked"
This error causes the domain you going to be added failed. The problem is due to server hostname is similar to the domain that you’re going to add.
The solution is very simple. Login to WHM & do the following
Server Configuration → Tweak Setting → Domains → Allow users to park subdomains of the server’s hostname main domain → Select On → Click Save Button
After you did this try to add the domain again. You should be able to add it successfully.